Calling multiple key value argument functions, does not work when the dict's keys are in unicode

[Jan Flyborg]

Hi,

I don't know if this is a known limitation (honestly I haven't made much effort googling around either), but the following works in Python 2.7, but not in Cython:

    def foo(*a, **k):
        print k

    dict = {u"arg1": "Hello World!"}

    foo(**dict)

When executed I get the following output just as expected:

    {u'arg1': 'Hello World!'}

But when compiled with Cython 0.16 and 0.17b3, I get the following:

    TypeError: foo() keywords must be strings

The culprit seems to be the unicode value for the dict's key. If changed to an ordinary string it works.

Jan Flyborg

[Stefan Behnel]

Jan Flyborg, 29.08.2012 20:46:

Hmm, yes, that was changed in CPython 2.6. It was explicitly forbidden
before. I'll see if I can adapt the keyword type checking code in Cython.

Thanks for the report!

Stefan

[Stefan Behnel]

Stefan Behnel, 29.08.2012 21:21:

I pushed a fix here:

https://github.com/cython/cython/commit/a8f70e2210b9a36c3b67ce5f426000c62473b62e

Note that this doesn't currently work in PyPy. It checks keyword types on
the caller side instead of the callee side (as CPython and Cython do).

Stefan

[Jan Flyborg]

Thank you. I'll try it out tomorrow.

I just found another problem in the same area. The same caveat applies for this one too (i.e I don't know if it is a known limitation or not, so please bare with me).

If you define a simple module test.py, like this:

    def foo(arg):
        print arg

And you call it like this from another module in CPython 2.7

    import test
    d = {"arg": "Hello World!"}
    test.foo(**d)

You get the result:

    Hello World!

However, if you compile test.py with Cython, and call it in the same way, you get:

    TypeError: foo() takes no keyword arguments

A simple workaround is probably to make 'arg' a keyword argument (haven't tried it), but this does not seem to be in line with how CPython works.

-- Jan Flyborg

[Stefan Behnel]

Jan Flyborg, 30.08.2012 00:35:

> If you define a simple module test.py, like this:
>
> def foo(arg):
> print arg
>
> And you call it like this from another module in CPython 2.7
>
> import test
> d = {"arg": "Hello World!"}
> test.foo(**d)
>
> You get the result:
>
> Hello World!
>
> However, if you compile test.py with Cython, and call it in the same way,
> you get:
>
> TypeError: foo() takes no keyword arguments
>
> A simple workaround is probably to make 'arg' a keyword argument (haven't
> tried it), but this does not seem to be in line with how CPython works.

Yes, that's a known optimisation. It's simply faster not to accept keyword
arguments for one-arg functions, and the use case of passing them is so
rare that we chose to optimise against it.

You can enable support with a compiler directive:

http://docs.cython.org/src/reference/compilation.html?highlight=always_allow_keywords#compiler-directives

Stefan

[Jan Flyborg]

Thank you once again. It worked like a charm when I added this compiler directive.

-- Jan Flyborg